Abstract
Bacteria entrapped in biofilms are a source of recurring problems in food processing environments. We recently developed a robust, 7-day biofilm microplate protocol for creating biofilms with strongly adherent strains of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella serovars that could be used to examine the effectiveness of various commercial sanitizers. Listeria monocytogenes 99-38, E.coli O157:H7 F4546, and Salmonella Montevideo FSIS 051 were determined from prior studies to be good biofilm formers and could be recovered and enumerated from biofilms following treatment with trypsin. Extended biofilms were generated by cycles of growth and washing daily, for 7 days, to remove planktonic cells. We examined five different sanitizers (three used at two different concentrations) for efficacy against the three pathogenic biofilms. Quaternary ammonium chloride (QAC) and chlorine-based sanitizers were the least effective, showing partial inhibition of the various biofilms within 2 h (1–2 log reduction). The best performing sanitizer across all three pathogens was a combination of modified QAC, hydrogen peroxide, and diacetin which resulted in ~6–7 log reduction, reaching levels below our limit of detection (LOD) within 1–2.5 min. All treatments were performed in triplicate replication and analyzed by one way repeated measures analysis of variance (RM-ANOVA) to determine significant differences (p < 0.05) in the response to sanitizer treatment over time. Analysis of 7-day biofilms by scanning electron microscopy (SEM) suggests the involvement of extracellular polysaccharides with Salmonella and E. coli, which may make their biofilms more impervious to sanitizers than L. monocytogenes.
Highlights
Sanitary practices in food manufacturing facilities target the elimination of pathogens and reduction of contaminating microbiota that gain access to the processing environment, often from the raw material and food ingredients, and from workers, drains, and ventilation ducts [1,2,3,4].Manufacturing shifts may process raw food ingredients for up to 8 h continuously
E. coli O157:H7 F4546, L. monocytogenes 99-38, and Salmonella Montevideo FSIS 051 were previously screened by a microplate fluorescence adherence assay differentiating them from other strains by their high-level adherence to form biofilms [19,38,39]
Examination of the data for the various sanitizers on the biofilms used in this study demonstrates differences between the effect on L. monocytogenes 99-38 vs. E. coli F4546 and S
Summary
Sanitary practices in food manufacturing facilities target the elimination of pathogens and reduction of contaminating microbiota that gain access to the processing environment, often from the raw material and food ingredients, and from workers, drains, and ventilation ducts [1,2,3,4].Manufacturing shifts may process raw food ingredients for up to 8 h continuously. Attachment may not be a completely random process, but rather may involve preferential attachment to sites that improve the chance of sustaining the development of biofilm [11] These may involve various adhering chemistries of the external bacterial architecture, such as hydrophilic/hydrophobic attractions from charged amino acids of flagella and pilli, or of carbohydrates and lipids [12,13,14]. They may occur, biofilms in food manufacturing facilities can lead to contaminated foods, resulting in outbreaks and illnesses among consumers [15]
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